This invention relates to fluid actuators, and is more particularly concerned with a device that responds to fluid pressure by bending. This invention is more specifically concerned with a steering section that can be disposed, e.g. at a distal tip of an elongated probe such as a video borescope or optical borescope. However, the invention can be broadly applied to pressure gauges, rotary actuators, and grabbers for remote tools.
A borescope or similar flexible probe can be generally configured as an elongated flexible insertion tube with a viewing head at its distal or forward end and a control housing for controlling or steering the distal or forward end. The typical borescope has a bendable tubular steering section or articulation section at the distal end adjacent the viewing head. The steering section typically comprises a series of alternating wobble washers and spacers, with control cables that extend through the wobble washers and then through the remainder of the flexible insertion tube. The steering cables connect with a steering control unit in the control section. Each such pair of cables is differentially displaced to bend the steering section in a bending plane. In this manner, the viewing head can be remotely oriented to facilitate the inspection of an object. Borescopes are often required to bend in narrow, tortuous passageways, so the radical dimension of the borescope is often quite limited, i.e., 6 mm diameter. Also, the pathway to the object or target can be quite long, which then requires the insertion tube and the steering cables to be rather long, e.g., fifteen feet or more.
A number of cable-actuated articulation or steering mechanisms are known, and typical ones are discussed in U.S. Pat. Nos. 3,610,231; 3,739,770; 3,583,393; 3,669,098; 3,779,151; and 4,347,837. Another steering mechanism is described in U.S. Pat. No. 4,700,693.
These cable-actuated articulation mechanisms require the cables to have a significant amount of slack or play because bends and coils in the insertion tube effectively shorten the cables and because the articulation section bends at discrete points rather than following a smooth arc. However, in many applications the articulation section must bend rather precisely to penetrate the tortuous passages into the area to be inspected without damaging delicate engine parts. For these reasons, cable tension must be limited and cable slack must be minimized. Moreover, where the insertion tube is long, extra cable slack is often included to accommodate the increased cable tightening due to the substantial coiling and bending of the insertion tube through which the steering cables pass.
A proposed arrangement to permit steering cables to be kept short as possible is described in U.S. Pat. No. 4,794,912. That patent described a braid-and-bladder pneumatic or hydraulic "muscle," i.e., linear traction motor, that addresses many of the problems found in these prior-art steering mechanisms. Specifically, fluid dynamic muscles mounted adjacent the distal end of the insertion tube are actuated by pneumatic or hydraulic pressure supplied through small flexible tubes within the borescope insertion tube. Short steering cables connect the respective muscles with the articulation mechanism. As fluid pressure is applied differentially to a pair of muscles, the cables move differentially and the articulation mechanism bends the steering section a desired amount.
While this system avoids many of the above-mentioned problems, especially those associated with extremely long cables, there are residual problems because of the reliance on an otherwise conventional cable steering mechanism. The steering section is rather complex and expensive, and does not follow a natural arc, as mentioned before. Further simplification, by replacing the cable driven steering mechanism, should reduce or eliminate these residual drawbacks, but a suitable alternative steering mechanism has eluded those in the art.